The IUPAC name of the coordination compound [CoCl2(en)2]+ is :

The correct answer is Option (4) → Dichloridobis (ethane - 1, 2-diamine) Cobalt (III)

A coordination entity is named by these IUPAC rules: the ligands are named first, in alphabetical order, then the metal with its oxidation state in Roman numerals. Anionic ligands end in -ido, so Cl⁻ is chlorido. Multiplying prefixes (di, tri, bis, tris) are ignored when alphabetising; bis is used for ligands whose names already contain a number, such as ethane-1,2-diamine (en).

First find the oxidation state of cobalt. The complex ion is \( \ce{[CoCl2(en)2]+} \); chloride is −1 and en is neutral:

    \( \displaystyle x + 2(-1) + 2(0) = +1 \Rightarrow x = +3 \)

Now order the ligands: chlorido (c) comes before ethane-1,2-diamine (e). Adding the prefixes gives dichlorido and bis(ethane-1,2-diamine). So the name is dichloridobis(ethane-1,2-diamine)cobalt(III).

Why the other options are incorrect

• Option (1) Dichlorobis (ethane 1, 2-diamine) Cobalt (III) — Incorrect. The order and the oxidation state are right, but the chloride ligand is named chlorido, not chloro, in the IUPAC names used in NCERT.

• Option (2) Dichlorido ethylene diammine Cobalt (I) — Incorrect. “Ammine” is the name of the \( \ce{NH3} \) ligand, the two en ligands need the prefix bis, and cobalt is +3, not +1.

• Option (3) Dichlorodiethylene diammine Cobalt (III) — Incorrect. The oxidation state is right, but chloride must be chlorido, “diammine” would mean two \( \ce{NH3} \) ligands, and en is named bis(ethane-1,2-diamine).

NCERT (2026-27 edition):
Naming of Mononuclear Coordination Compounds – “… The ligands are named in an alphabetical order before the name of the central atom/ion. (This procedure is reversed from writing formula). … Prefixes mono, di, tri, etc., are used to indicate the number of the individual ligands in the coordination entity. When the names of the ligands include a numerical prefix, then the terms, bis, tris, tetrakis are used, the ligand to which they refer being placed in parentheses. … Oxidation state of the metal in cation, anion or neutral coordination entity is indicated by Roman numeral in parenthesis.”

Note: The same/similar question has been asked in different years by NTA as per the details given below: